I have one of these:
http://www.robertdyas.co.uk/P~138092~Draper-Stud-Detector-and-Distance-Estimator
And I was debating the feasibility of opening it up and trying to get an output from it to use in an arduino program, if you've done anything like this or know anything about how such devices work I'd be grateful for the help!
-Jack
One well known way to hack these is to "emulate" the display. Capture the data send to the display to get the readings.
It is a laser based tool, so be careful - http://www.tooled-up.com/artwork/ProdPDF/DRA88988ins.pdf -
update
not laser based , see below or datasheet 
400364:
I have one of these:http://www.robertdyas.co.uk/P~138092~Draper-Stud-Detector-and-Distance-Estimator
And I was debating the feasibility of opening it up and trying to get an output from it to use in an arduino program, if you've done anything like this or know anything about how such devices work I'd be grateful for the help!
-Jack
That link didn't give much information, but I would bet that it is ultrasonic in nature; it likely won't be easy to "interface" to, unless it has some kind of hackable serial interface (it is difficult to even wonder on this without opening it up first). Likely, any on-board processing and LCD interfacing is done via an epoxy-blobbed ASIC, and it won't be very straightforward to interface with it. If you are lucky, the driver system for the ultrasonics is external to the ASIC (likely) and you can reverse engineer that (perhaps to the point of getting it to "ping" and listen for the return, resulting in an analog voltage level being read?). However, if you don't have the tools or understanding on how to do this (an oscilloscope would go a long way towards helping), it probably isn't worth it.
Think about this: You can purchase from many suppliers very inexpensive ultrasonic ranging sensors (many for less than $10.00 USD); is that really worth the time and effort you would have to go thru to hack this (unless that is your intention - but then again, such a device would have to be cheaper than $10.00 USD for it to make much sense).
@robtillaart: The device doesn't measure distance using a laser: it is ultrasonic, and says so in the manual you posted...
@cr0sh, you're right, I read some other page were it was declared laser and I copied that without checkin the datasheet good enough 
robtillaart:
@cr0sh, you're right, I read some other page were it was declared laser and I copied that without checkin the datasheet good enough
Don't feel bad about it; they didn't make things very clear anywhere, and even in the manual there's a seeming "undertone" that it is using the laser for something; I had to read it fairly carefully to find the bit about it being ultrasonic!
I was pretty certain it was, though; while there are a couple of sub-$200.00 USD laser-based distance measuring devices out there (and those use a linear sensor and triangulation), neither is that cheap...
Don't feel bad about it;
I don't, just playing 
It was just another learning experience ...